5. 去掉and 或把which改成it　 6. 去掉it

3. where----which/that　　 4. which前加入in 或which 改成that 或/

1. when-which/that　 2. holidays后加入when

6. The reason why he missed the speech was that he forgot the time.

5. The reason why Peter failed was his laziness.

4. Is this the house that/which we visited last year?

3. Is this the house where/in which Lincoln once lived?

2. I will never forget the days which/that we spent together in Paris.

1. I will never forget the days when/on which we worked together.

10. It was a prison from which no one escaped.